Linux driver for 1394 OHCI controller voluntarily flushes isoc context
when total size of accumulated context header reached PAGE_SIZE. This
kicks tasklet for the isoc context. This is inconvenient to process
runtime of PCM substream.
This commit adds a restriction of the maximum size of PCM period to
avoid this behaviour.
Signed-off-by: Takashi Sakamoto <o-takashi@xxxxxxxxxxxxx>
---
sound/firewire/amdtp-stream.c | 29 ++++++++++++++++++-----------
1 file changed, 18 insertions(+), 11 deletions(-)
diff --git a/sound/firewire/amdtp-stream.c b/sound/firewire/amdtp-stream.c
index fd7c3e4d5374..8a7818130382 100644
--- a/sound/firewire/amdtp-stream.c
+++ b/sound/firewire/amdtp-stream.c
@@ -176,6 +176,8 @@ int amdtp_stream_add_pcm_hw_constraints(struct amdtp_stream *s,
struct snd_pcm_runtime *runtime)
{
struct snd_pcm_hardware *hw = &runtime->hw;
+ unsigned int ctx_header_size;
+ unsigned int maximum_usec_per_period;
int err;
hw->info = SNDRV_PCM_INFO_BATCH |
@@ -196,19 +198,24 @@ int amdtp_stream_add_pcm_hw_constraints(struct amdtp_stream *s,
hw->period_bytes_max = hw->period_bytes_min * 2048;
hw->buffer_bytes_max = hw->period_bytes_max * hw->periods_min;
- /*
- * Currently firewire-lib processes 16 packets in one software
- * interrupt callback. This equals to 2msec but actually the
- * interval of the interrupts has a jitter.
- * Additionally, even if adding a constraint to fit period size to
- * 2msec, actual calculated frames per period doesn't equal to 2msec,
- * depending on sampling rate.
- * Anyway, the interval to call snd_pcm_period_elapsed() cannot 2msec.
- * Here let us use 5msec for safe period interrupt.
- */
+ // Linux driver for 1394 OHCI controller voluntarily flushes isoc
+ // context when total size of accumulated context header reaches
+ // PAGE_SIZE. This kicks tasklet for the isoc context and brings
+ // callback in the middle of scheduled interrupts.
+ // Although AMDTP streams in the same domain use the same events per
+ // IRQ, use the largest size of context header between IT/IR contexts.
+ // Here, use the value of context header in IR context is for both
+ // contexts.
+ if (!(s->flags & CIP_NO_HEADER))
+ ctx_header_size = IR_CTX_HEADER_SIZE_CIP;
+ else
+ ctx_header_size = IR_CTX_HEADER_SIZE_NO_CIP;
+ maximum_usec_per_period = USEC_PER_SEC * PAGE_SIZE /
+ CYCLES_PER_SECOND / ctx_header_size;
+
err = snd_pcm_hw_constraint_minmax(runtime,
SNDRV_PCM_HW_PARAM_PERIOD_TIME,
- 5000, UINT_MAX);
+ 5000, maximum_usec_per_period);
if (err < 0)
goto end;
--
2.20.1
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